This invention relates generally to suspension systems for scrapers and, more particularly concerns suspension systems which will dampen the shock loads during transport while acting as rigid connections during the digging operations of the vehicle.
The function of a scraper vehicle is to uniformly and efficiently remove a layer of earth from one section of land and transport the earth to another section. During the removal process the vertical attitude of the scraper bowl must be locked at a specified height to insure uniform earth removal. This locking of the bowl position is normally accomplished through the use of hydraulic jacks which connect the tractor to the bowl. However, during the transporting procedure the flexibility of the tires, the great weight of the vehicle and its carried load and the speed of transport all combine to produce a bouncing movement of the entire vehicle. This bouncing causes high loads on the structural members, decreases the control which the operator has over the vehicle's motion and increases the operator's discomfort by jarring him severely.
The existing systems which attempt to control the bounce during transporting utilize gas compression to cushion the load transferred between the bowl and the tractor. By using gas compression to control the bounce of the vehicle, the effectiveness of the existing systems are limited by the inherent physical characteristics of gas compression. The first such limitation is the expense and the limited durability caused by the complexity of the physical components necessary to separate the hydraulic fluid from the gas in the system while keeping the gas system responsive to the hydraulic system. The second limitation is the limited effectiveness of the cushioning action that results from the heat generated in the compressing of the gas increasing the temperature of the gas system which increases the pressure of the gas system, thereby stiffening the connection between the bowl and the tractor by unnecessarily increasing the normally constant spring rate of the system. The third limitation of the gas compression cushioning systems is their marginal acceptability resulting from the doubling of the spring rate when the transporting is done with a loaded bowl. Under these conditions a series of accumulators must be used to provide increased spring rates according to the load carried by the bowl, but the load carrying spring rate is still substantially constant and does not allow for variations in the weight of the carried material.
Accordingly, it is the primary aim of the present invention to provide a lockable suspension system for a scraper which eliminates the transport bounce thereby improving the operator's comfort and decreasing the structural loads on the supporting members.
More particularly, it is object of the invention to provide a suspension system which has a spring rate that is at most nominally effected by temperature variations.
Moreover, an object of the present invention is to have a scraper suspension which functions in both loaded and unloaded conditions while responding to weight variation in the loaded condition.
Finally, an object of the present invention is to have a scraper system whose durability is not effected by the vehicle's rugged working environment or by incompatibility between the bowl control medium and the cushioning medium.